According to electromagnetic theories, wave guides can be used to transmit electromagnetic waves, which can be converted into electrical current signals through the use of metal pins installed in the interior of the wave guides. As shown by FIGS. 1A and 1B, one end of a rectangular wave guide is closed which forms a back short plane at the interior, and a metal pin is installed perpendicular to the length of the wave guide and at a distance of 1/4 .lambda.g. (.lambda.g is the wavelength). Therefore, vertical electromagnetic waves transmitted from the other end of the rectangular wave guide can be converted into electrical current signals for subsequent electrical applications.
However, the configuration, as shown in FIGS. 1A and 1B, can only receive vertically polarized electromagnetic wave signals. In order to simultaneously receive vertically and horizontally polarized signals, one possible implementation is shown in FIGS. 2A and 2B. A cylindrical wave guide employs separate vertical and horizontal pins to receive separately the vertically and horizontally polarized signals. However, since these two pins are on the same plane as the back short plane and at a distance of 1/4 .lambda.g from the back short plane, as the vertical pin receives the vertically polarized signals, simultaneously some of the horizontally polarized signals are collected. During applications, it is hoped that horizontal signals collected by the vertical pin are kept to a minimum. This is also true for the horizontal pin collecting vertical signals. In other words, the degree of isolation between signals should be kept to a maximum. As shown in FIGS. 2A and 2B, the two pins are located on the same plane (at a reflective distance of 1/4 .lambda.g from the back short plane); this is also where the reflective signals are at the strongest. Thus, the vertical pin not only receives vertical signals, but also receives the strongest horizontal signals. Although by positioning the directions of the double pins, a certain degree of signal isolation can be achieved (approximately 15-20 dB). There is still a need for improvement.